Many types of implantable medical devices (IMDs) have been clinically implanted over the last twenty years that deliver relatively high-energy cardioversion and/or defibrillation shocks to a patient's heart when a malignant tachyarrhythmia, e.g., atrial or ventricular fibrillation, is detected. Cardioversion shocks are typically delivered in synchrony with a detected R-wave when fibrillation detection criteria are met, whereas defibrillation shocks are typically delivered when fibrillation criteria are met and an R-wave cannot be discerned from the EGM.
The current state of the art of ICDs or implantable pacemaker/cardioverter/defibrillators (PCDs) includes a full featured set of extensive programmable parameters which includes multiple arrhythmia detection criteria, multiple therapy prescriptions (for example, stimulation for pacing in the atrial, ventricular and dual chamber; atrial and ventricular for bradycardia; bi-atrial and/or bi-ventricular for heart failure; and arrhythmia overdrive or entrainment stimulation) and high level stimulation for cardioversion and/or defibrillation, extensive diagnostic capabilities and high speed telemetry systems. These full-featured ICDs or PCDs, hereinafter IMD, are typically implanted into patients who have had, and survived, a significant cardiac event (such as sudden death). Additionally, these devices are expected to last up to 5-8 years and/or provide at least 200 life saving therapy shocks.
Even though there have been great strides in size reduction over the past 20 years, the incorporation of all these features in an IMD, including the longevity requirements, dictates that the devices be typically much larger than current state of the art pacemakers. Such devices are often difficult to implant in some patients (particularly children and thin, elderly patients) and typically require the sacrifice of 1 or 2 veins to implant the lead system because leads associated with the implantation of an IMD utilize a transvenous approach for cardiac electrodes and lead wires. The defibrillator canister/housing is generally implanted as an active can for defibrillation and electrodes positioned in the heart are used for pacing, sensing and detection of arrhythmias.
Although IMDs and implant procedures are very expensive, most patients who are implanted have experienced and survived a sudden cardiac death episode because of interventional therapies delivered by the IMDs. Survivors of sudden cardiac death episodes are in the minority, and studies are ongoing to identify patients who are asymptomatic by conventional measures but are nevertheless at risk of a future sudden death episode. Current studies of patient populations, e.g., the MADIT II and SubQ ICD HeFT studies, are establishing that there are large numbers of patients in any given population that are susceptible to sudden cardiac death, that they can be identified with some degree of certainty and that they are candidates for a prophylactic implantation of a defibrillator (often called primary prevention). However, implanting currently available IMDs in all such patients would be prohibitively expensive. Further, even if the cost factor is eliminated there is shortage of trained personnel and implanting resources.
One option proposed for this patient population is to implant a prophylactic subcutaneous implantable cardioverter/defibrillator (SubQ ICD) such that when these patients receive a shock and survive a cardiac episode, they will ultimately have an implant with a full-featured ICD and transvenous leads.
While there are a few small populations in whom SubQ ICD might be the first choice of implantation for a defibrillator, the vast majority of patients are physically suited to be implanted with either an ICD or SubQ ICD. It is likely that pricing of the SubQ ICD will be at a lower price point than an ICD. Further, as SubQ ICD technology evolves, it may develop a clear and distinct advantage over ICDs. For example, the SubQ ICD does not require leads to be placed in the bloodstream. Accordingly, complications arising from leads placed in the cardiovasculature environment is eliminated. Further, endocardial lead placement is not possible with patients who have a mechanical heart valve implant and is not generally recommended for pediatric cardiac patients. For these and other reasons, a SubQ ICD may be preferred over an ICD.
Therefore, for these and other reasons, a need exists for a simplified, cosmetically and ergonomically adaptive SubQ ICD that can be implanted beneath the skin and over the ribcage. Specifically, the SubQ ICD should be implantable with minimal trauma in a wide range of patients by surgeons employing conventional surgical instruments and monitoring equipment so as to make the implantation process less expensive and more widely available.
The present invention describes several SubQ ICD configurations adapted for subcutaneous implant. The SubQ ICD's of the present invention would be capable of delivering a limited number of shocks at maximal shock energy with an additional capability to provide pacing therapy for temporary post shock cardiac support or bradycardia pacing.